This research deals with a further investigation of the possible role of altered autonomic function in patients with essential hypertension. Studies will be directed toward determining whether there is any significant alteration of the blood levels or urinary excretion of the catecholamines in patients with labile or fixed essential hypertension. The etiology of the enhanced pressor response to norepinephrine will be studied in hypertensive patients in order to determine whether this is related to an intrinsic vascular phenomenon or whether it reflects altered metabolism and thereby higher levels of circulating catecholamines after infusion. The physiological and autonomic responses to stress will be studied in both normals and hypertensive patients and a correlation will be sought between the state of autonomic activity in hypertensive patients and their response to specific forms of antihypertensive therapy.